Ultrasonic probe with ultrasonic transducers addressable on common electrical channel

ABSTRACT

Methods and apparatus are provided for electrically addressing multiple ultrasonic transducers that are connected to a common electrical channel and housed within an imaging probe. An imaging probe may comprise an imaging ultrasonic transducer and a moveable element for controlling the direction of an emitted imaging beam, and an angle sensing ultrasonic transducer, where the angle sensing ultrasonic transducer is configured for determining the direction of an ultrasonic imaging beam. The angle-sensing transducer may be configured to direct an angle sensing ultrasonic beam towards an acoustically reflective substrate and provide a signal by detecting a reflected ultrasonic beam reflected from the acoustically reflective substrate, where the acoustically reflective substrate is positioned relative to the movable element such that motion of the movable element produces a change in the signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/437,758, titled “IMAGING PROBE WITH ULTRASONIC TRANSDUCERSADDRESSABLE ON COMMON ELECTRICAL CHANNEL” and filed on Jan. 31, 2011,the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to imaging systems and probes employingultrasonic imaging transducers. The present disclosure also relates tomethods of detecting changes in the angular orientation of movableelements employed for directing radiation from imaging transducersduring minimally invasive imaging procedures. High resolution biomedicalimaging serves numerous purposes, including assessing tissue structuresand anatomy, planning and/or guiding interventions on localized regionsof the body, and assessing the result of interventions that alter thestructure, composition or other properties of a region.

High frequency ultrasound, in particular, has found significant use inintracardiac and intravascular applications. For these applications,ultrasound transducers are incorporated into a catheter or other devicethat can be inserted into a lumen or cavity within the body. Twoimportant implementations of high frequency ultrasound are intravascularultrasound (IVUS) for imaging blood vessels, and intracardiacechocardiography (ICE) for imaging cardiac chambers. Both ICE and IVUSare minimally invasive, and involve placing one or more ultrasoundtransducers inside a blood vessel or cardiac chamber to take highquality images of these structures.

Courtney et al. (US Patent Application Publication No. US20090264768)describe an intravascular/intracardiac echocardiography catheter capableof forward viewing via 3D ultrasound and/or optical imaging. This isachieved using a movable member to image at various angles. This devicebenefits from knowledge of the position and/or orientation of either theimaging mechanism itself or of a deflecting element, such as a mirror.

In order to correlate the images obtained using an imaging transducerwith the orientation of the imaging probe, it is important to provide amechanism for determining the relative angular orientation of themovable portion of an imaging system. This angular orientationdetermines an angle at which imaging energy is transmitted and/orreceived from the imaging probe. Courtney et al. disclose a number ofangle detection mechanisms and methods. One method involves relating therotational speed to the imaging angle, for example, using a look-uptable. A series of electronic and electromechanical techniques are alsodescribed, including capacitive, resistive, electromagnetic, inductive,and strain gauge based techniques. Also described are techniques thatemploy diffuse scattering from a reflector using the primary imagingsource. Also disclosed are optical and acoustic methods and mechanismthat utilize a detection sensor that is separate from the primaryimaging source to determine the imaging angle.

There are a number of limitations related to the techniques describedabove. For example, the use of a lookup table relating rotational speedto imaging angle may be prone to significant inaccuracy. Differentorientations or situations may influence the relationship betweenimaging angle and rotational speeds. This may occur as a result ofgravitational forces in different orientations, different temperatureconditions, or stress on the catheter among others. Also, manytechniques—predominantly those using modalities other than the imagingmodality—may require the addition of significant complex components andenergy sources.

SUMMARY

Methods and apparatus are provided for electrically addressing multipleultrasonic transducers that are connected to a common electrical channeland housed within an imaging probe. An imaging probe may comprise animaging ultrasonic transducer and a moveable element for controlling thedirection of an emitted imaging beam, and an angle sensing ultrasonictransducer, where the angle sensing ultrasonic transducer is configuredfor determining the direction of an ultrasonic imaging beam. Theangle-sensing transducer may be configured to direct an angle sensingultrasonic beam towards an acoustically reflective substrate and providea signal by detecting a reflected ultrasonic beam reflected from theacoustically reflective substrate, where the acoustically reflectivesubstrate is positioned relative to the movable element such that motionof the movable element produces a change in the signal.

Accordingly, in a first aspect, there is provided an imaging probecomprising: a longitudinal body; a first ultrasonic transducer providedwithin the longitudinal body, wherein the first ultrasonic transducer islocated remote from a proximal end of the longitudinal body, and whereinthe first ultrasonic transducer is configured to deliver an ultrasonicimaging beam to a region outside of the longitudinal body and to receivereflected ultrasonic imaging energy from the region; a second ultrasonictransducer housed within the longitudinal body; and electricallyconductive paths extending through the longitudinal body and defining acommon electrical channel; wherein the first ultrasonic transducer andthe second ultrasonic transducer are connected to the common electricalchannel, and wherein the common electrical channel is electricallyconnectable to an image processing system.

In another aspect, there is provided an ultrasonic probe comprising: alongitudinal body; a first ultrasonic transducer provided within thelongitudinal body, wherein the first ultrasonic transducer is locatedremote from a proximal end of the longitudinal body, and wherein thefirst ultrasonic transducer is configured to deliver an ultrasonic beamto a region outside of the longitudinal body; an additional ultrasonictransducer provided within the longitudinal body; an electricallyconductive paths extending through the longitudinal body and defining acommon electrical channel; wherein the first ultrasonic transducer andthe additional ultrasonic transducer are connected to the commonelectrical channel, and wherein the common electrical channel iselectrically connectable to an external processing system.

In another aspect, there is provided an ultrasonic angle detectiondevice for determining an angle of a pivotable member, wherein thepivotable member is pivotally coupled to a solid support, the devicecomprising: an electrically addressable ultrasonic transducer attachedto the pivotable member, wherein the ultrasonic transducer is configuredto emit ultrasonic pulses in a direction that is dependent on anorientation of the pivotable member; and an acoustically reflectivesubstrate fixed relative to the solid support and having a surfacecurvature selected to substantially retroreflect the ultrasonic pulsesback to the ultrasonic transducer over a defined angular range of thepivotable member, such that a distance between the ultrasonic transducerand the acoustically reflective substrate, as determined along a beampath of the ultrasonic pulses, varies over the angular range.

A further understanding of the functional and advantageous aspects ofthe disclosure can be realized by reference to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure will now be described, by way of exampleonly, with reference to the drawings, in which:

FIG. 1 is a schematic of an imaging system including ultrasound andoptical components.

FIG. 2 is a perspective drawing of a flexible imaging probe with anadapter, conduit, and imaging assembly.

FIG. 2a is a cross sectional view of the mid-section of the imagingprobe of FIG. 2 taken along the dotted line.

FIG. 2b is a magnified and expanded drawing of the distal region of theimaging probe of FIG. 2.

FIGS. 3a-3g describe embodiments of techniques for causing tilting of atiltable member.

FIG. 3a shows a longitudinal cutaway of a catheter in which the tiltingis caused by centripetal motion.

FIG. 3b shows a cross-sectional cutaway of the catheter shown in FIG. 3a.

FIG. 3c shows the catheter of FIG. 3a and the resulting tilting causedby rotating the scanning assembly at a faster rate than that of FIG. 3a.

FIG. 3d shows a cross-sectional cutaway of the catheter shown in FIG. 3c.

FIG. 3e shows a longitudinal cutaway of a catheter in which the tiltingis controlled using one or more magnets.

FIG. 3f shows a cross-sectional cutaway of the catheter in FIG. 3 e.

FIG. 3g shows the catheter of FIG. 3e and the resulting deflectioncaused by magnetism.

FIG. 3h shows a cross-sectional cutaway of the catheter in FIG. 3 g.

FIG. 3i shows a potential scanning pattern for generating 3D images withimaging angle information.

FIG. 3j illustrates a control system in which the angle sensingtransducer is employed to provide feedback for controlling a directionof the emitted imaging beam.

FIG. 3k shows an implementation of a system using a torsional spring asa restoring mechanism.

FIG. 4 demonstrates the use of a high frequency ultrasound transducer toestimate the tilt angle of a tiltable ultrasound transducer using a timeof flight method. FIGS. 4a and 4b show the measurement of the tilt ofthe tiltable component at two different angular orientations. FIGS. 4cand 4d plot the time dependence of the transmitted and receivedultrasonic pulses for the angular orientations shown in FIGS. 4a and 4b, respectively. FIG. 4e plots the dependence of the time delay of theultrasonic beam on the tilt angle.

FIGS. 5a and 5b show connection schemes of ultrasound transducers toproduce acoustic energy through multiple ultrasound transducers via asingle electrical connection. FIG. 5a shows a case where an imagingtransducer and an angle detection transducer are directly bondedtogether. FIG. 5b shows a case where an imaging transducer and an angledetection transducer are physically separated, but connectedelectrically. FIGS. 5c-5e illustrate embodiments in which two imagingultrasonic transducers are housed within a sheath and connected to acommon electrical channel for simultaneous imaging in antiparallel (FIG.5c ) and orthogonal (FIGS. 5d-5e ), and parallel (FIG. 5f ). FIG. 5gshows a three-frequency imaging arrangement; and FIG. 5h shows anarrangement with a two-frequency assembly combined with an opticalimaging modality. FIG. 5i shows an arrangement with focused ultrasoundtransducers.

FIG. 6 shows a separation between the active bandwidths of twoultrasound transducers connected to a common channel.

FIG. 7 shows the use of tuning elements for the two ultrasoundtransducers using separate RLC circuits for each of the transducers.

FIGS. 8a-8e demonstrates the use of a high frequency ultrasoundtransducer to estimate the deflection of a tiltable optical and/oracoustic mirror. FIGS. 8a and 8b show the measurement of the tilt angleof the tiltable mirror at two different angular orientations. FIGS. 8cand 8d plot the time dependence of the transmitted and receivedultrasonic pulses for the angular orientations shown in FIGS. 8a and 8b, respectively. FIG. 8e plots the dependence of the time delay of theultrasonic beam on the deflection angle.

FIGS. 9a-9e demonstrate the use of a high frequency ultrasoundtransducer to estimate the angular orientation of an ultrasoundtransducer mounted on a deformable member. FIGS. 9a and 9b show themeasurement of tilt of the mirror at two different angular orientations.FIGS. 9c and 9d plot the time dependence of the transmitted and receivedultrasonic pulses for the angular orientations shown in FIGS. 9a and 9b, respectively. FIG. 9e plots the dependence of the time delay of theangle detecting ultrasonic beam on the tilt angle.

FIGS. 10a-10e demonstrate the use of a high frequency ultrasoundtransducer to estimate the deflection angle of a tiltable componentusing a method that assesses the intensity of the received signal. FIGS.10a and 10b show the measurement of the tilt of a tiltable component attwo different angular orientations. FIGS. 10c and 10d plot the timedependence of the transmitted and received ultrasonic pulses for theangular orientations shown in FIGS. 10a and 10b , respectively. FIG. 10eplots the dependence of the peak voltage relating to the receivedultrasonic beam on the deflection angle.

FIGS. 11a and 11b show (a) the use of a surface comprising a specularreflector in comparison with (b) a diffuse reflector. FIGS. 11c and 11dplot the time dependence of the transmitted and received ultrasonicpulses for the angular orientations shown in FIGS. 11a and 11b ,respectively.

FIGS. 12a-d demonstrate the use of two high frequency ultrasoundtransducers to estimate the deflection angle of a tiltable componentusing a time of flight method, shown in (a) and (b) at two differentangular orientations. FIGS. 12c and 12d plot the time dependence of thetransmitted and received ultrasonic pulses for the angular orientationsshown in FIGS. 12a and 12b , respectively.

FIGS. 13a-e show a disc with curved features to increase the range ofangles that can be detected using a time of flight method, shown in (a)and (b) at two different angular orientations. FIGS. 13c and 13d plotthe time dependence of the transmitted and received ultrasonic pulsesfor the angular orientations shown in FIGS. 13a and 13b , respectively.FIG. 13e plots the dependence of the time delay of the ultrasonic beamon the deflection angle.

FIGS. 14a-d show the use of an ultrasound transducer that diffuselyemits and detects ultrasound energy to increase the range of angles thatcan be detected using a time of flight method, shown in (a) and (b) attwo different angular orientations. FIGS. 14c and 14d plot the timedependence of the transmitted and received ultrasonic pulses for theangular orientations shown in FIGS. 14a and 14b , respectively.

FIGS. 15a-d show the use of a curved surface to increase the range ofangles that can be detected with improved precision using a time offlight method with an angle detection transducer attached to a tiltablecomponent, shown in (a) and (b) at two different angular orientations.FIGS. 15c and 15d plot the time dependence of the transmitted andreceived ultrasonic pulses for the angular orientations shown in FIGS.15a and 15b , respectively. FIG. 15e illustrates the relationshipbetween the curvature of the surface and the orientation of thetransducer, such that the surface is locally approximately normal to theincident acoustic beam to ensure strong received signals.

FIGS. 16a-d show the use of a high frequency ultrasound transducer toestimate the tilt angle of a tiltable ultrasound transducer mechanicallycoupled to an otherwise acoustically passive component with the angledetection transducer mounted on the otherwise acoustically passivecomponent, shown in FIGS. 16a and 16b at two different angularorientations. FIGS. 16c and 16d plot the time dependence of thetransmitted and received ultrasonic pulses for the angular orientationsshown in FIGS. 16a and 16b , respectively. FIG. 16e shows some geometricrelationships that can be used to calculate the tilt angle from theknowledge of the distance between angle detection transducer and aconstant distance between a point on each of two tiltable components.

FIGS. 17a-d show the use of a high frequency ultrasound transducer toestimate the deflection angle of a tiltable ultrasound transducermechanically coupled to an acoustically passive component with an angledetection transducer integrated onto an imaging transducer. FIGS. 17cand 17d plot the time dependence of the transmitted and receivedultrasonic pulses for the angular orientations shown in FIGS. 17a and17b , respectively.

FIGS. 18a-b show the use of the curved surface shown in FIG. 15 with amechanically coupled acoustically passive component similar to thatshown in FIGS. 16 and 17. FIG. 18a shows a view with the sameperspective shown in FIG. 17. FIG. 18b shows a view cut through thehatched line from FIG. 18 a.

FIGS. 18c-18i show an embodiment in which the position of the mechanicalcoupler is detected using the angle detection transducer to estimate theangle of deflection. FIGS. 18c and 18e show the tiltable member at twodifferent positions. FIGS. 18d and 18f show views cut through thehatched line from FIGS. 18c and 18e respectively. FIGS. 18g and 18h showtiming diagrams from the scenarios described in FIGS. 18d and 18frespectively. FIG. 18i shows a relationship between the received timedelay and the tilt angle.

FIGS. 19a-g show a sample pulse sequence and corresponding receivedsignal from both the imaging transducer and the deflection angletransducer on a single channel using multiple methods. FIG. 19a showsthe measurement of two features, and FIG. 19b shows how the signals fromthe two features and the signal from the angle detection transducer canbe extracted based on an interleaved pulsing scheme.

FIG. 19c shows an example using either or both of: prior knowledge ofdistance ranges and using spectral methods. FIG. 19d shows how thesignals from the two features and the signal from the angle detectiontransducer can be extracted based on whether or not they are beyond themaximum distance range used in the angle detection scheme. FIG. 19eshows an example of the use of spectral methods to separate angledetection information from imaging information.

FIG. 19f shows a transmit pulse sequence where multiple imaging pulsesare transmitted between single angle detection pulses. FIG. 19g shows atransmit pulse sequence where there is a long time delay between theimaging pulse and the subsequent angle detection pulse, and a short timedelay between the angle detection pulse and the subsequent imagingpulse.

FIGS. 20a-b show different estimation methods for determining a distanceas detected by an angle detection transducer. FIG. 20a shows an exampleof the detection of the distance based on the use of radio-frequency(RF) peak detection methods and envelope detection methods, while FIG.20b example illustrates the detection of the distance based on the useof cross correlation methods.

FIG. 21 shows experimental data obtained from an angle detectionexperiment conducted with the embodiment described in FIGS. 18a and 18b.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosure will be described withreference to details discussed below. The following description anddrawings are illustrative of the disclosure and are not to be construedas limiting the disclosure. Numerous specific details are described toprovide a thorough understanding of various embodiments of the presentdisclosure. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present disclosure. It should be understood that theorder of the steps of the methods disclosed herein is immaterial so longas the methods remain operable. Moreover, two or more steps may beconducted simultaneously or in a different order than recited hereinunless otherwise specified.

As used herein, the terms, “comprises” and “comprising” are to beconstrued as being inclusive and open ended, and not exclusive.Specifically, when used in the specification and claims, the terms,“comprises” and “comprising” and variations thereof mean the specifiedfeatures, steps or components are included. These terms are not to beinterpreted to exclude the presence of other features, steps orcomponents.

As used herein, the term “example” means “serving as an example,instance, or illustration,” and should not be construed as preferred oradvantageous over other configurations disclosed herein.

As used herein, the terms “about” and “approximately”, when used inconjunction with ranges of dimensions of particles, compositions ofmixtures or other physical properties or characteristics, are meant tocover slight variations that may exist in the upper and lower limits ofthe ranges of dimensions so as to not exclude embodiments where onaverage most of the dimensions are satisfied but where statisticallydimensions may exist outside this region. It is not the intention toexclude embodiments such as these from the present disclosure. Forexample, in embodiments of the present disclosure, dimensions ofcomponents of the imaging probe are given but it will be understood thatthese are not meant to be limiting.

As used herein, the term “high resolution imaging” generally refers tooptical imaging methods and high frequency ultrasound, the latter ofwhich typically involving frequencies of greater than 3 MHz, and moretypically involving frequencies in the range of 5 to 100 MHz.

As used herein, the terms “imaging radiation” and “imaging energy” referto electromagnetic or acoustic radiation, or both. Specifically,electromagnetic radiation may span the ultraviolet, visible, and orinfrared spectrum of wavelengths.

As used herein, the term “deflect” refers to a change in at least anangular orientation of an object relative to. In one example, adeflection may be a change in the tilt of a tiltable component or achange in an angular orientation of a movable member. As used herein,the term “tilt” refers to the angular orientation of an object. A changein angular orientation, as defined by a change in a tilt angle, may berelative to another portion of an object if the object is deformable, orrelative to another object within an assembly of objects. For example, acomponent mounted on a pivot mechanism may tilt by pivoting around anaxis of the pivot mechanism. Alternatively, a component mounted on adeformable component or integrated as part of a deformable component mayexperience a tilt as a result of deformation of the deformablecomponent.

As used herein, the term “move” refers to a change in either an angularorientation of an object, a position of an object or both the angularorientation and position of an object. For example, the movement of anobject may occur as a result of a tilting an object or pivoting of anobject around an axis. Movement may also occur as a result of adeformation an object or a deformable portion of an object. Movement mayalso occur as a result of translation of an object. The movement of anobject may be in absolute terms, relative to another portion of anobject if the object is deformable, or relative to another object withinan assembly of objects.

As used herein, the term “electrical channel” refers electricallyconductive paths that are suitable for delivering electrical energy to,or detecting electrical signals from, an electrical element, such as anultrasonic transducer. An example of an electrical channel includes twoconductors, such as wires, that are contacted with an electrical elementsuch that when a voltage difference is applied between the conductors, acorresponding voltage is applied across the electrical element.

Embodiments of the disclosure provide apparatus and methods for thenon-contact detection of a change in orientation or position of amovable member. An ultrasonic transducer is employed to generate anincident ultrasonic beam and to detect a reflected ultrasonic beam,where the deflection of a deflectable member produces a change in one ormore of: a) the intensity, b) the time delay, or c) the spectral contentof the reflected beam. The proceeding disclosure describes andillustrates, through examples, the application of various embodiments tominimally invasive imaging systems and methods. However, it is to beunderstood that these applications are merely non-limiting examples, andthe embodiments disclosed here are applicable and adaptable to a widerange of uses and applications.

Before describing example embodiments and their application to minimallyinvasive imaging systems, a brief review of minimally invasive imagingsystems is provided with reference to FIGS. 1 to 3, by way of example.Referring first to FIG. 1, an imaging system is shown at 10 comprisingimaging probe 44, which connects via patient interface module 36 toimage processing and display system 49. Image processing and displaysystem 49 includes hardware to support one or more imaging modalities,such as ultrasound, optical coherence tomography, angioscopy, infraredimaging, near infrared imaging, Raman spectroscopy-based imaging, orfluorescence imaging. Specific embodiments of ultrasonic imaging probesand combined ultrasonic and optical imaging probes are disclosed byCourtney et al. in US Patent Publication No. 20080177183, titled“Imaging Probe with Combined Ultrasounds and Optical Means of Imaging”and filed on Jan. 22, 2008, US Patent Publication No. 20080177138,titled “Scanning Mechanisms for Imaging Probe” and filed on Jan. 22,2008 and US Patent Publication No. 20090264768, titled “ScanningMechanisms for Imaging Probe” and filed on Mar. 27, 2009, each of whichare incorporated herein by reference in their entirety.

Controller and processing unit 34 is employed to facilitate thecoordinated activity of the many functional units of the system, and maycontain some or all of the components shown in the Figure and listedherein. An operator interacts with system 50 via display and/or userinterface 38. System 10 may further include electrode sensors 40 toacquire electrocardiogram signals from the body of the patient beingimaged. The electrocardiogram signals may be used to time theacquisition of imaging data in situations where cardiac motion may havean impact on image quality. The electrocardiogram may also serve as atrigger for when to begin an acquisition sequence, such as when to beginchanging the speed of rotation of a motor in order to cause a desiredscan pattern to take effect. For example, electrocardiogram triggeredinitiation of an imaging sequence may enable images to be acquiredduring a particular phase of the cardiac cycle, such as systole ordiastole.

Optical subsystem 30, if included in a particular implementation of animaging system, may include any or all of the following components:interferometer components, one or more optical reference arms, opticalmultiplexors, optical demultiplexers, light sources, photodetectors,spectrometers, polarization filters, polarization controllers, timingcircuitry, analog to digital converters, parallel processing arrays andother components known to facilitate any of the optical imagingtechniques. Ultrasound subsystem 32 may include any or all of thefollowing components: pulse generators, electronic filters, analog todigital converters, parallel processing arrays, envelope detectors,amplifiers including time gain compensation amplifiers and othercomponents known to facilitate acoustic imaging techniques.

Controller and processing units 34, if included in a particularimplementation of the imaging system, serve multiple purposes. Thoseskilled in the art will appreciate that specific components requireddepend on the needs of a particular type of imaging system. For example,controller and processing units may include any combination of a motordrive controller, data storage components (such as memory, hard drives,removable storage devices, readers and recorders for media such as CDs,DVDs, and Bluray™ discs), position sensing circuitry and/or software,angle detection circuitry and/or software, timing circuitry and/orsoftware, cardiac gating functionality, volumetric imaging processors,scan converters and others. As noted above, display and user interface38 is also optionally provided for either real time display or displayof data at a time later than the time at which imaging data is acquired.

It is to be understood that patient interface module 36 and controllerand processing units 34 are but one example illustration of theselection and organization of hardware subsystems, and that many otherimplementations are possible. For example, patient interface module 36may be housed with controller and processing units 34 within processingand display system 49.

Example imaging probe 44 includes an imaging assembly 50, optionalimaging conduit 46 along a substantial portion of its length, andconnector 48 at its proximal end 47. Imaging assembly 50 is located neardistal end 41 of imaging probe 44. Imaging assembly 50 generally refersto the components of the imaging probe 44 from which the signals (eitheracoustic, optical or both) are collected for the purposes of imaging aregion that is proximate to imaging assembly 50. Imaging assembly 50 mayhouse transducers for transmitting and/or receiving imaging radiation.The emitter and receiver may be a single component, as is often the casewith a piezoelectric transducer.

In the case of optical imaging, imaging assembly 50 typically containsthe distal tip of a fiber optic, as well as a combination of opticalcomponents such as a lens (for instance, a ball lens or a GRIN lens). Amirror and/or prism may be included for use in beam delivery and/orcollection. Optionally, there may be an optical detector, such as a CCDarray, or an optical light source, such as one or more LEDs,incorporated directly in the imaging assembly that may obviate the needfor one or more fiber optics in an optical imaging probe.

Imaging probe 44 may contain ports at one or more points along itslength to facilitate flushing. Moreover, imaging assembly 50, connector48 and/or imaging conduit 46 may be filled and/or surrounded with afluid such as saline, and may be flushed. In applications involvingoptical imaging, imaging probe 44 may be filled with a gas. The gas mayinclude carbon dioxide or another readily dissolved gas with minimalbiotoxicity. Alternatively, in the case of a multimodal optical/acousticimaging system, imaging assembly 50 may be compartmentalized to includeat least one gas-filled compartment or lumen for optical imaging and atleast one fluid filled compartment or chamber for acoustic imaging.

Imaging conduit 46 includes at least one conductive wire (optionally twoor more) that connect an emitter and/or receiver via connection to anadapter, herein referred to as patient interface module 36. Imagingconduit 46 may include a fiber optic, for example, wrapped by two layersof electrical wire that are electrically insulated from one another.Imaging conduit 46 may further be reinforced by other structuralfeatures, such as helically wrapped wires or other designs used toconstruct imaging torque cables for rotating scan mechanisms.Alternatively, imaging conduit 46 may contain electrical conductors, anda rotational mechanism may be located remote from the proximal end forimparting rotary motion to the imaging assembly. One example mechanismincludes a micro-motor and a slip ring in close proximity to the imagingassembly.

The imaging probe 44 may optionally include memory, such as an EEPROMfor storing information including calibration information, serialinformation, probe design information, desired filter information, andany other probe specific information. This memory may reside inconnector 48.

Patient interface module 36 facilitates transmission of signals withinany fibers and/or wires to the appropriate image processing units. Itmay contain a motor drive unit for imparting rotational motion to thecomponents of the imaging mechanism.

Additional sensors may be incorporated as part of patient interfacemodule 36, such as position sensing circuitry, for example, to sense theangle of rotation of a rotary component within the imaging probe 44and/or for detecting the angle of deflection of a member at the distalend 41 of the imaging probe 44. Additionally, patient interface module36 may include amplifiers to improve the transmission of electricalsignals or power between the imaging probe 44 and the rest of thesystem.

In many applications, it can be important to optimize the geometry of aminimally invasive probe so that it is as small as reasonably possibleto achieve its desired purpose. Current IVUS and ICE probes areapproximately 0.9 to 4 mm in diameter and the smaller sizes of probescan be delivered more distally within the vascular tree of the coronaryanatomy as the vessel caliber tapers down or as diseased vessels arestenosed. Furthermore, within the cardiac anatomy, smaller probes (suchas those with a diameter less than about 3.4 mm) can be readily advancedacross the atrial septum into the left atrium of the heart. Thus,smaller sizes generally allow for interrogation of a larger portion ofthe coronary or cardiac anatomy. It is therefore desirable for a probeand its components to be contained within a minimal outer diameter toenable imaging, such as using imaging performed with the scanningmechanisms described by Courtney et al. (US Patent ApplicationPublication No. 20080177138).

FIG. 2 is a perspective drawing of a flexible catheter containing fiberoptic 66 and co-axial electrical cable 68. The proximal connectorcontains fiber optic connection joint 60 that can be received by patientinterface module 36 to optically couple imaging fiber optic 66 to imageprocessing and display system 49. Electrical connectors 62 allow one ormore electrical conduits to be connected to the ultrasound circuitryand/or controller and processing units. In applications in which theimaging conduit rotates around its longitudinal axis, there may be aneed to couple the rotating components of the imaging fiber optic with arelatively stationary fiber optic that connects to image processing anddisplay system 49. This coupling can be achieved with the use of a fiberoptic rotary joint incorporated either as part of the proximal connectorof imaging probe 48 or as part of patient interface module 36.Similarly, there may need to be a mechanism for coupling the rotatingcomponents of the electrical system with relatively stationaryelectrical components that connect to image processing and displaysystem 49. This can be achieved through the use of one or moreelectrical slip rings or slip ring channels.

FIG. 2a shows a cross sectional view of the middle section of thecatheter shown in FIG. 2 taken along the dotted vertical line. The crosssection shows the optional fiber optic 66, optional guidewire 52,imaging conduit lumen 47, external sheath 43, which is a hollow,flexible elongate shaft made of physiologically compatible material andhaving a diameter suitable to permit insertion of the hollow elongateshaft into bodily lumens and cavities, and co-axial wiring 68. Theexpanded detailed view of the end of the imaging probe 44 in FIG. 2bshows the imaging assembly 50 which optionally includes a tiltablemember 51, distal end of the optional guidewire 52 extended beyond theend of the external sheath 43 and a flush port 53 near the end of thesheath 43. In FIG. 2, the proximal end of the imaging probe 44 includesan optional guidewire port 56 into which the guidewire 52 is insertedand the connector assembly 48 includes a flush port 58 and electricalcontacts 62 along with the connector body. An optional guidewire port 54is seen in FIG. 2 b.

FIGS. 3a-d show an example catheter that employs a tiltable member forscanning an imaging beam. FIG. 3a shows a perspective cutaway drawing ofthe distal region of an imaging probe 44 that relies on centripetalforce to generate the change in tilt angle of the tiltable member 51.Imaging probe 44, which includes a sheath 43 for isolation from bodilyfluids and cavities, includes tiltable member 51 housed within imagingassembly 50.

Tiltable member 51 is mounted on pins 102, about which tiltable member51 is free to pivot. As imaging conduit 46 and assembly 50 (not shown)are rotated about longitudinal axis 59 at a slow rate (indicated byarcing hatched arrow 61), the angle α subtended between longitudinalaxis 59 and tiltable member 51 is relatively small. A cutawayperspective cross-sectional view of FIG. 3a is shown in FIG. 3b . FIG.3c shows a similar drawing of the distal region of imaging probe 44 asshown in FIG. 3a , except with imaging conduit 46 being rotated at afaster rate (indicated by arcing hatched arrow 63) than in FIG. 3a .Centripetal force causes tiltable member 51 to tilt such that there isan increase in the angle α subtended between the longitudinal axis ofthe catheter and the tiltable member 51. FIG. 3d is a cutawayperspective cross-sectional view from FIG. 3 c.

FIG. 3e shows a perspective cutaway drawing of the distal region of arelated imaging probe 44 that relies on the use of dynamicallycontrolled magnetic fields to change the deflection angle of tiltablemember 51. Imaging probe 44, which may include a sheath 43 for somedegree of isolation from bodily fluids and cavities, includes tiltablemember 51 comprising part of the imaging assembly 50. Tiltable member 51is mounted on pins 102, about which the tiltable member 51 is free topivot. Mounted on the tiltable member 51 is a magnetically influencedelement 109 that can be either attracted or repulsed by a magneticfield. For example, it may be a ferromagnetic component, or a permanentmagnetic component. Element 109 may integrally be part of tiltablemember 51, such as if all or a portion of element 109 is made of eithera ferromagnetic or magnetic substrate. An electromagnetic component 107is also placed at a position separate from the tiltable member 51. Theelectromagnetic component can be controlled to produce attractive orrepulsive forces relative to magnetically influenced component 109. Inso doing, the angle α subtended between the longitudinal axis 59 of thecatheter and the tiltable member can be adjusted as desired.Furthermore, similar imaging probes may be conceived that involveinterchanging the position of the electromagnetic component 107 andmagnetically influenced component 109, or using two electromagnetsinstead of an electromagnet and a magnetically influenced component. Acutaway perspective cross-sectional view of FIG. 3e is shown in FIG. 3f.

FIG. 3g shows a similar drawing of the distal region of imaging probe 44as shown in FIG. 3e , except with a repulsive sequence applied toelectromagnet 107 such that the angle α subtended by tiltable member 51is increased. FIG. 3h is a cutaway perspective cross-sectional view fromFIG. 3 g.

Tiltable member 51 may be an ultrasonic transducer, such as anultrasound transducer used for producing B-scan ultrasound images.Another embodiment includes an ultrasound transducer mounted on atiltable member.

FIG. 3i shows an example of a potential scanning pattern for generatingultrasound images. In this case, the tiltable member is an ultrasoundimaging transducer 101. As imaging conduit 46 and assembly 50 arerotated at a constant rate, an image is generated along a surface thatapproximates a cone. As the rate of rotation is changed, centripetalforce causes the angle subtended between the longitudinal axis of thecatheter and ultrasound imaging transducer 101 to change resulting in aseries of concentric imaging cones 118 for different rotational speeds.The angle subtended between the longitudinal axis of the catheter and anaxis normal to ultrasonic imaging transducer 101 will be referred to asthe “imaging angle”. In this case, the transducer begins with arelatively small imaging angle θ1 implying a fast rate of rotationalspeed. As the rotational speed is reduced, the imaging angle isincreased to θ2.

In order to cause the imaging angle to return to a stable position inthe absence of rotation, a restoring mechanism can be used as shown inFIG. 3k . Here, the primary movable member 101 is connected to asecondary movable member 114 using a mechanical coupler 176, allowingthe two members 101 and 114 to move synchronously. All components arehoused within a shell 178. One or more springs 182 are connected betweenthe movable member 101 and the shell 178. The springs may be torsionsprings, linear springs, or a cantilever spring. The movable members 101and 114 are pivotally supported by around pins 111 and 113 respectively.This spring 182 provides a force to restore the member 101 to the sideviewing position in the absence of adequate rotational force to overcomethe restoring force provided by spring 182. In addition to adding amechanical restoring force, the torsional springs may also be formed, atleast in part, from an electrically conductive material, such asstainless steel, beryllium copper, copper, silver, titanium, gold,platinum, palladium, rhenium, tungsten, nickel, cobalt, alloys thatinclude one or more of these metals and many other metals and theiralloys can be used to provide electrical connections. Here, spring 182is in electrical communication with conductor 300. Conductor 301 makes asimilar connection to the opposite side of movable member 101 (notshown).

Alternatively a spring that provides both a restoring force and anelectrical connection may be made of more than one material, where onematerial provides conductive properties and another material providesmechanical properties for the restoring force. For example, a torsionspring may be formed of a nitinol core with a gold outer layer, appliedby sputtering, plating, evaporation, electroforming, electroplating,electron beam techniques or other methods known in the art.Alternatively, one or more of the materials may be a material other thana metal, such as a polymer.

The conducting elements of the spring have cross sectional dimensions ona micron scale (for example, less than about 100 microns×100 microns)using photolithography and related techniques. Gold hardened with cobaltand nickel cobalt provide further examples of suitable materials for aconductive spring with desired mechanical properties. A portion of thesurface of the spring may be covered by an insulating material, such asparylene, Teflon, polyimide and many others. Alternatively, theinsulating may occur by processing the outer surface of the spring, suchas by allowing an oxide to form on the outer surface of a metal oralloy.

Example embodiments described below provide ultrasonic apparatuses andmethods for combining multiple ultrasound transducers on a singleelectrical channel. One application that will be described in detailrelates to the fact that in order to accurately reconstruct a 3D imageof the imaging field, the imaging angle must be determined for a givenultrasound image acquisition event, vector, or pixel. As noted above,while the proceeding embodiments relate to applications involvingminimally invasive imaging, where angular detection is performed usingan apparatus mounted within an imaging assembly within an imaging probe,it is to be understood that these applications are merely non-limitingexamples that are provided for teaching purposes and are not intended tolimit the scope of the disclosed embodiments.

Referring now to FIG. 4, an ultrasonic angle detection apparatus isshown for detecting a change in angle of a tiltable member using a timeof flight detection method. Angle detection transducer 100 is placed ata fixed location relative to an initial position of tiltable member 101,which includes material that is at least partially acousticallyreflective relative to the acoustic transmission medium. Angle detectiontransducer 100 transmits ultrasonic beam 110 towards the tiltable member101. As the beam reaches the tiltable member 101, a portion of the beamis reflected back towards the angle detection transducer 100. Theacoustically reflective substrate may be configured to reflect orscatter components of the incident ultrasonic beam in a diffuse manner,as will be described in further detail below.

Tiltable member 101 may itself be acoustically reflective, or may haveattached to one or more of its surfaces, such as its back surface, anacoustically reflective substrate. As noted above, acoustic reflectionsmay be diffuse to support the detection of a reflected ultrasonic beamover a broad range of tilt angles (or imaging angles), and the reflectedultrasonic beam may be generated by surface reflection, volumereflection, or a combination thereof. In an example embodiment, tiltablemember 101 includes an imaging transducer that transmits an acousticbeam 120 in a direction away from the angle detection transducer 100. Itis not necessary that the angle detection mechanism only uses the backsurface of the tiltable member. It may be oriented and/or positioned touse any side or surface of the tiltable member as best suited for anyparticular embodiment.

FIGS. 4a and 4b show two different angular positions of tiltable member101, which is rotatable about pivot axis 102. In one example embodiment,the pivot axis is implemented using or more pins or a hinge alignedalong the pivot axis around which the tiltable member pivots. In FIG. 4a, the separation between tiltable member 101 and angle detectiontransducer 100 is greater than in FIG. 4b . This separation distanceresults in the angle detection beam 110 having a shorter time of flightin FIG. 4b than FIG. 4 a.

The tilt angle can be calculated with the time of flight and priorknowledge of the geometric configuration of the transducer and thetiltable component, including their relative locations in space andranges of motion, and the speed of sound in the acoustic path. Theacoustic beam for the angle detection transducer may travel through amedium such as water or saline, wherein the speed of sound isapproximately 1450 to 1600 m/s.

For example, if the angle is to be determined based on differences intime of flight, a baseline signal may be captured at a known angularposition and known estimated time of flight during an initializationphase. This baseline signal may be used as a comparator against signalsreceived at different positions to estimate tilt angle using thetechniques described above.

Alternatively, the tilt angle can be determined empirically based oncalibration measurements made with known angular deflections.Calibration measurements can be employed to produce a calibration curve,such as the curve shown in FIG. 4e . Such calibration data may be storedin an EEPROM provided within the imaging probe, as described above.

FIGS. 4c and 4d are timing diagrams that represent the signal detectedfor each angle scenario in FIGS. 4a and 4b , respectively. In theseexamples, a pulse 500 is transmitted from transducer 100 at time (t)=0and a received pulse is detected at a later time with a reducedmagnitude. The received pulse 502 corresponding to the signal reflectedfrom tiltable member 101, as oriented in FIG. 4a , has a greater timedelay than the received pulse 504 corresponding to the signal reflectedfrom tiltable member 101 in FIG. 4b . Furthermore, as acoustic wavespropagate through a medium, they are partially attenuated. Thisattenuation is frequency dependent with energy components in the higherfrequencies attenuated more than lower frequency energy components. As aresult of this, not only is the delay between received pulses changed,so too is the spectral content of the received pulse 504. In thisembodiment, a change in spectral content can also be related to the tiltangle.

The tilt angle determined using the above method may be employed forfeedback in a control system, as shown in FIG. 3j . A desired angle 194and the measured angle 192 (determined using the aforementioned method)are provided as inputs to controller 196, and the output of controller196 is provided to angle control mechanism 190. A variety of controlmethods and algorithms known in the art may be employed, including, butnot limited to, PID and fuzzy logic controllers.

In another example embodiment, the tiltable member is employed to directa beam of ultrasonic radiation from an imaging ultrasonic transducerhoused within an imaging probe, where the ultrasonic imaging transducerand the angle sensing transducer are electrically connected to a commonchannel for excitation and detection. The ultrasonic imaging transducermay form tiltable member 101, or alternatively may be mounted totiltable member 101, or may be fixed relative to tiltable member 101such that the imaging beam is reflected, scattered, and/or refracted bytiltable member 101 (as shown in embodiments described below).

By connecting both transducers to a common electrical channel, a simple,reliable, cost-effective, and space efficient system is realized.Furthermore, the ability to use a common electrical channel may minimizethe number of electrical connections that need to be made. For example,if the electrical connections to an ultrasound imaging transducermounted on or incorporated as tiltable member 101 are via wires orconductive springs from the housing of imaging assembly 50 to tiltablemember, the wires or springs will mechanically influence the ease withwhich tiltable member can tilt. It may be desirable to minimize thenumber of wires or springs between tiltable member 101 and the rest ofthe imaging assembly 50.

Using a common electrical channel for both an imaging transducer and anangle detection transducer reduces the number of electrical conductorsto the tiltable member and may thus provide more flexibility in thedesign and/or performance of the imaging probe. Similarly, using acommon electrical channel may reduce the number of channels that need tobe accommodated by the patient interface module 36 (the patientinterface module contains components, such as slip rings, that coupleelectrical signals between the rotating parts of the imaging probe andthe non-rotating parts of the image processing and display system 49).Similarly, using a common electrical channel may reduce the number ofanalog to digital converters or reduce the number or complexity of othersignal processing components in the image processing and display system49.

Furthermore, a common electrical channel may help optimize the size,configuration and/or number of electrical conductors in the imagingconduit. This would potentially improve the mechanical properties of theimaging conduit 46, such as improving the flexibility of the imagingconduit, reducing the amount of non-uniform rotational distortion,reducing the required size of the imaging conduit 46 or providing roomfor additional features to be incorporated into imaging probe 44.

It is to be understood that the present embodiments pertaining to theconnection of two or more ultrasonic transducers on a common electricalchannel are not intended to be limited to applications involving the useof one imaging transducer and one angle detection transducer. As furtherdescribed below, the common electrical connection of multiple ultrasonictransducers within a longitudinal body of an ultrasonic probe may beimplemented in a wide variety of applications, for which imaging andangle detection are illustrative yet non-limiting embodiments.

FIGS. 5a and 5b provide schematics illustrating two example embodimentsin which a single electrical channel is employed within imaging conduit46 as a source for both an imaging transducer 105 in the imaging probe44 and a second transducer, such as an angle detection transducer 100.

FIG. 5a shows the distal end of coaxial cable 302, where first andsecond conductive paths 300 and 301 are connected in parallel toultrasonic imaging transducer 105 and ultrasonic angle detectingtransducer 100. For minimally invasive imaging procedures, electricalcable 302 may be a micro-coaxial cable or micro twisted pair with adiameter of less than about 1000 microns, or alternatively less than 500microns. Excitation pulses are transmitted to both ultrasonictransducers along signal wire 301, while a second connection, optionallyto ground, is provided by second wire 300. The conductive paths of thechannel, labeled as the signal (+) and ground (GND) paths may beinterchanged. Both transducers are shown in a side view.

Imaging transducer 105 may be larger in size than angle sensingtransducer 100, and imaging transducer 105 may possess a lower centerfrequency than angle sensing transducer 100. In one exampleimplementation, the center frequency of imaging transducer 105 may be inthe range of 5-60 MHz, while the center frequency of angle detectiontransducer 100 may be in the range of 25-100 MHz. In another exampleembodiment, the transducers differ in center frequency by a factor of atleast about 2.5. In one embodiment, the factor is between about 2.5 and3. In one specific and non-limiting example, one transducer may have acenter frequency of 15 MHz, and the other transducer may have a centerfrequency greater than about 40 MHz.

Imaging transducer 105 generally consists of a piezoelectric material319, commonly PZT-5H, but may include other piezoelectric ceramics, acomposite design, a single crystal design, lithium niobate, PVDF and avariety of other materials known for ultrasound transducer fabrication,including cMUT and pMUT transducers. The piezoelectric is coated on bothsides 318 and 320 with conductive layers, such as thin layers of gold orother materials with high conductivity. On one side of the piezoelectriclayer 319, a backing layer 321 may be applied to dampen undesiredacoustic signals from going through the back of the transducer. Thebacking layer 321 may be electrically conductive, as this simplifies anelectrical connection with angle detection transducer 100, as willbecome apparent below. In an alternative embodiment in which the entirebacking layer 321 and/or backing layer 310 is not electricallyconductive, suitable electrically connections between signal wire 301,conductive layer 320, and conductive layer 311, may be provided througha conductive channel formed within backing layer 321 and/or backinglayer 310 or through a conductive wire connecting the conductiveregions. The signal conduction wire 301 is connected electrically toconductive layer 320, such as through a conductive backing layer 321.Alternatively, other conductive paths between signal conduction wire 301and conductive layer 320 can be used. In the example embodiment of FIG.5a , all regions sharing the electrical connection to the signalconduction wire 301 are labeled with a “+” symbol. At one end of thetransducer backing layer 321, an electrically insulating barrier 331 isbonded to the transducer. On the face of the piezoelectric material 318opposite the backing layer 321, a thin layer of an electricallyconductive acoustic impedance matching material 317 is bonded.

A thin and electrically conductive layer 316 is bonded adjacent to theelectrically insulated barrier 331. Ground connection 300 is connectedelectrically to this layer. All regions sharing the electricalconnection to the ground conduction wire 300 are labeled as “GND”. Theacoustic beam emitted from the imaging transducer is directed along anaxis normal to the transducer surface 392.

Similar to the design of the imaging transducer 105, angle detectiontransducer 100 consists of a piezoelectric material 312, commonlyPZT-5H, but may often include a composite design, a single crystal,lithium niobate, or PVDF and a variety of other materials known in theart. Piezoelectric layer 312 is coated on both sides 311 and 313 with athin conductive layer, commonly gold. On one side of piezoelectric layer312, a backing layer 310 is applied to damp out undesired acousticsignals from going through the back of the transducer. Backing layer 310may be electrically conductive and electrically connected to backinglayer 321. At one end of the transducer backing complex, a thinelectrically insulated barrier 330 is bonded to the transducer. On theface of the piezoelectric material 312 opposite backing layer 310, athin layer of an electrically conductive acoustic impedance matchingmaterial 314 is bonded. A thin electrically conductive layer 315 isbonded adjacent to the electrically insulated barrier 330. The acousticbeam emitted from angle detecting transducer 100 is directed along anaxis normal to the transducer surface 394. Alternatively, backing layer310 may be omitted and conductive layer 311 may be directly bonded tobacking layer 321. In this case, the two transducers may share backinglayer 321 for damping out unwanted acoustic signals.

In order for the transducers to share electrical connections in anembodiment in which the transducers form a unitary structure, they maybe mounted or bonded such that the conductive ground channels 315 and316 of each transducer are in direct electrical contact, theelectrically insulating barriers 330 and 331 are in continuity, and thebacking layers 310 and 321 of both transducers are electricallyconductive and in direct contact with each other. There should be highelectrical resistance between the electrically conductive signal regionsand ground regions of either transducer in order to maintain appropriateconnections.

It is to be understood that the embodiment described in FIG. 5a isexample of one of several embodiments wherein two ultrasound transducerscan share a single electrical channel and form a unitary structure. Inan alternative embodiment, one or more of the backing layers need not beelectrically conductive, provided that conductive pathways to opposingsides of piezoelectric elements 312 and 319 for each of the transducersare provided. Electrically conductive pathways can be made usingmaterials such as wires, metals, conductive epoxies and other materialsknown in the art. The pathways may be made using processes such as, butnot limited to, layering, bonding, and soldering, sputtering, wirebonding.

Acoustic matching layers 314 and 317 may improve the efficiency ofacousto-electric coupling but may not be necessary for one or more ofthe transducers. In an alternative embodiment, a plurality of matchinglayers may be used for one or more of the transducers. Furthermore,electrically insulating barriers 330 and 331 provide example embodimentsfor electrically isolating the signal and ground pathways from eachother but may take on more complex arrangements than described in FIG.5a , and may include a void or gap made of an insulating gas or liquidrather than a solid material. Furthermore, the signal and grounddesignations of each side of the two transducers are arbitrary and canbe connected in several permutations of arrangements.

FIG. 5b illustrates an embodiment for sharing a single electricalconnection between the angle detection transducer 100 and imagingtransducer 105 while the two transducers do not form a unitarystructure. For example, the transducers may be fabricated in the sameway as described in reference to FIG. 5a , but are not bonded together.Instead, the signal connection 301 and ground connection 300 fromcoaxial cable 302 are connected electrically to opposing sides of thepiezoelectric elements 313 and 319 both the angle detection transducer100 and the imaging transducer 105. In the example shown in FIG. 5b ,all regions sharing the electrical connection to the signal conductionwire 301 are labeled with a “+” symbol. Similarly, the ground connection300 is connected electrically to both the conductive path 315 on theangle detection transducer 100 and the conductive path 316 on theimaging transducer 105. All regions sharing the electrical connection tothe ground conduction wire 300 are labeled as “GND” in FIG. 5b . In oneexample embodiment, the ultrasound transducers operate at substantiallydifferent center frequencies.

In some embodiments, a multi-transducer imaging probe is provided inwhich the imaging probe houses two or more ultrasonic imagingtransducers that are connected to a common electrical channel. Eachtransducer may be selected to exhibit a unique spectral response that issubstantially spectrally distinct and non-overlapping from the otherultrasonic transducers. As noted above, additional electrical filteringmay be employed to provide additional spectral isolation among theultrasonic transducers.

The imaging transducers may be positioned to direct each ultrasonicimaging beam in a distinct direction, thereby enabling simultaneousimaging at multiple angles. Unlike phased array imaging, in whichmultiple ultrasonic transducers are driven in a phased relationship byunique and individual electrical channels, the present embodimentenables multi-transducer, multi-angle and/or multi-frequency imagingbased using a single electrical channel upon which the signals forexciting the different transducers are multiplexed.

In one example embodiment, two or more imaging transducers may beoriented to direct their ultrasonic imaging beams in a substantiallycommon direction, which may be useful, for example, for simultaneousimaging in multiple acoustic spectral windows. In other embodiments, asshown below, three or more transducers can be used to form unitarystructures similar to those shown in FIGS. 5c and 5d , and that multipletransducers can be oriented at arbitrary angles with respect to eachother.

FIGS. 5c and 5d show two example embodiments in which an imaging probehouses two imaging transducers oriented with a relative angle of 180°and 90°, respectively. Transducers 399 and 397 are electricallyconnected via common coaxial conductor 302 (comprising common groundwire 300 and common signal wire 301), and are shown as housed withinsheath 43. Connections to the suitable conductive layers of transducers397 and 399 may be made, for example, as shown in FIG. 5a . It should benoted that conductive paths within the unitary structure can beconfigured such that conductive paths 300 to 301 connect to a commonside of the unitary structure, or in various other arrangements suchthat the electrical connections within the unitary structure provideappropriate conductive paths to transducers 397 and 399. In otherexample implementations, the connections to the conductive layers of thetransducers may be made, as described above, using materials such aswires, metals, conductive epoxies and other materials known in the art,and pathways may be made using processes such as, but not limited to,layering, bonding, soldering, sputtering, wire bonding.

FIG. 5c demonstrates a catheter housed in a sheath 43 configured forside-viewing imaging with a unitary structure formed by joiningultrasound transducers 397 and 399. Here, transducers 397 and 399transmit anti-collinear beams, 393 and 395 respectively, in a generallyside viewing direction relative to the longitudinal axis of thecatheter. Upon a complete revolution of the distal imaging assembly,both transducers will have imaged the same region in tissue. Thisarrangement may be useful in a situation where it is desired to imagethe same region of tissue with two different frequencies, often a lowfrequency for deep penetration and a higher frequency to achieve highresolution. While this embodiment shows beams 393 and 395 beinganti-collinear, other useful embodiments would include beams that areanti-parallel, but not necessarily anti-collinear.

Similarly, FIG. 5d shows an example implementation in which ultrasoundimaging transducers 397 and 399 are both in a generally side viewingdirection while transmitting substantially orthogonally directed beamswith the centers of the transducer apertures positioned at approximatelythe same position along the probe's longitudinal axis. Upon a completerevolution of the distal imaging assembly, both transducers will haveimaged the same region in tissue.

FIGS. 5c and 5d provide two non-limiting embodiments of imaging probeshousing dual transducers that are electrically addressable via a commonelectrical channel, for which many other related embodiments and designvariations are possible. For example, any of the embodiments of thepresent disclosure involving tiltable, pivotable, rotatable and movableelements for directing an emitted imaging beam may be adapted to furtherinclude a second imaging transducer according to the present embodiment,where the second imaging transducer need not necessarily be physicallycontacted with the first imaging transducer.

In some embodiments, the second imaging transducer may be positioned ororiented to have a field of view remote from the first imagingtransducer. Alternatively, the first and second imaging transducers mayhave fields of view that overlap to create a combined field of view,wherein the signals from one transducer may be used to provideultrasound data for one portion of the combined field of view andsignals from the second transducer are preferentially used to provideultrasound data for another portion of the combined field of view.Ultrasound data from each of the one or more transducers may be used forany of several purposes, including imaging, tissue characterization,sensing of instruments outside the imaging probe, and sensing movementof components within the image probe.

For example, in the embodiments shown in FIGS. 5c and 5d , a transducerwith a first center frequency may be used for imaging more distantregions in the combined field of view, while a second transducer with alower center frequency than the first transducer may be used forproviding higher resolution imaging data in regions closer to theimaging catheter. Furthermore, such embodiments may optionally includeone or more angle sensing ultrasonic transducers for detecting thedirection of an ultrasonic imaging beam emitted by the first and/orsecond imaging transducers, where the angle sensing transducers are alsoconnected to the common electrical channel.

FIG. 5e shows a scenario where one imaging transducer 387 is shaped suchthat it contains features that allow for the mounting of a secondtransducer 397 at an oblique angle relative to the longitudinal axis ofthe imaging probe. When the distal imaging assembly is rotated,transducer 387 will image a largely side-viewing region of tissue, whiletransducer 397 will image a partially forward viewing conical region oftissue.

FIG. 5f shows a configuration of a unitary structure of multipleultrasound transducers driven on a single channel suitable forsituations where multiple collinear imaging beams are desired. In theembodiment show in the Figure, a lower-frequency beam 389 is transmittedfrom transducer 391 in parallel with a higher-frequency beam 392 fromtransducer 397. Transducer 397 also receives corresponding echoes.

The embodiment shown in FIG. 5f may be employed for second orderultrasound field (SURF) imaging. SURF imaging uses acoustic energy intwo distinct frequency bands transmitted simultaneously. The energy inone frequency band is generally at a low frequency (a center frequencyin the range of 0.5-10 MHz) and is used as a modulation or manipulationpulse. The energy in the high frequency band tends to be centeredapproximately 7-10 times higher than the center frequency of the lowfrequency band. The high frequency energy band is employed to image thetissue under different modulation pressures, as generated but themodulation or manipulation pulse. Accordingly, referring to FIG. 5f ,ultrasound transducer 397 may be employed to provide a high frequencyimaging beam, while larger ultrasound transducer 391 may be provided togenerate a SURF ultrasound beam that is parallel and substantiallycollinear to the imaging beam. While this technique has been performedwith two separate ultrasound transducers with two separate electricalchannels, the present embodiment may be performed to achieve SURFimaging with a single electrical channel.

It may also be desirable to include more than two imaging transducers onthe same unitary structure connected by a single electrical channel.FIG. 5g shows a configuration including three ultrasound transducers,each of which is characterized by a different center frequency. Anexample of an application for such an embodiment is again for SURFimaging. A low frequency manipulating beam 389 is transmitted fromtransducer 391 and used to modulate tissue being imaged, while a higherfrequency imaging beam 392 is emitted from transducer 397 in a directionthat is collinear to modulating beam 389. Positioned to create anantiparallel, and, in some embodiment, anti-collinear, beam 381 isanother transducer 379. The frequency of beam 381 may be selected to behigher than that of imaging beam 392 to provide high resolution imaging.One example of a suitable set of frequencies is a 3 MHz modulating beam389, a 25 MHz SURF imaging beam 392, and a 60 MHz high frequency imagingbeam 381.

It may also be desirable to combine multi-frequency transducers withother imaging modalities. One potential family of modalities is fibercompatible optical imaging modalities. These may include opticalcoherence tomography, fluorescence imaging, photoacoustic imaging,angioscopy, Raman spectroscopy and other optical modalities known in theart. FIG. 5h shows one such configuration including a unitary structurehaving three components: (1) an ultrasound transducer 399 having a firstcenter frequency, (2) a second ultrasound transducer 397 having a secondcenter frequency that is different from the first center frequency, withboth ultrasonic transducers connected to a common electrical channel,and (3) an optical imaging system 383 configured to generate opticalimaging beam 385. In the example embodiment shown in the Figure, thesecond ultrasound transducer 397 contains a hole and an optical beamdirector to allow optical imaging beam 385 to emerge substantiallycollinear with second ultrasound imaging beam 395.

While the imaging transducers shown in FIG. 5 are shown as flattransducers, one or more of them may be curved to provide beam focusing.In many applications, it may be beneficial to provide a focusedultrasound beam, or beams, for improved lateral resolution at a desireddepth. It may specifically be desirable to focus higher frequencyultrasound beams at regions of interest that are closer to the imagingassembly, and to focus lower frequency ultrasound beams at regions ofinterest further from the imaging assembly. This enables lateralresolution high resolution images at multiple depths, giving aneffectively improved depth of field. In this case, the highest lateralresolution would be achieved close to the imaging probe, where it isoften desired for a number of imaging or image guided procedures such ascrossing CTOs, vulnerable plaque detection, or transseptal puncture. Anembodiment showing focused transducers is shown in FIG. 5i , where afirst, low frequency transducer 373 is curved to focus at a depth 375with acoustic beam 374. A second, high frequency transducer 376 has itsacoustic beam 377 focused to a depth 378, which is closer to the imagingprobe than 375. There are multiple ways of achieving focus on anultrasound transducer, including using acoustic lenses, mechanicalpressing, machining of a curved surface, or using a flexiblepiezoelectric such as PVDF or a composite material that can be formedinto a curved surface.

As noted above, in some example embodiments, excitation pulses anddetected signals are respectively transmitted to and received from bothtransducers on a common electrical channel, while enabling the detectedsignals from each transducer to be separated or demultiplexed for imageprocessing and/or angle determination. There are numerous techniquesthat can achieve this without departing from the scope of the presentembodiment. Selected techniques involve separating the frequency spectraof the imaging signal information and the angle detection signalinformation.

One embodiment for demultiplexing both detected signals is illustratedin FIG. 6. The center frequencies of both transducers are selected suchthat there is substantially little or no overlap between the respectivetransducer spectral bandwidth ranges 396 and 398. If the transducers areadequately separated in terms of frequency spectra, signals from onetransducer will not interfere with signals from the other. That is, inthe illustrative context of an embodiment involving an imagingtransducer 105 and an angle detection transducer 100, an imaging pulsesent to the imaging transducer 105 will not cause a significant acousticresponse from the angle detection transducer 100.

Common definitions of spectral bandwidth in ultrasound are based on therange of frequencies surrounding a peak amplitude of the frequencydomain representation of an acoustic or electrical signal generated ordetected by an ultrasound transducer. In one embodiment, the spectralbandwidths are at least 6 dB bandwidths. For example, the 6 dB spectralbandwidth typically refers to the range of frequencies surrounding afrequency of a peak amplitude in which the amplitude of the signalacross that range of frequencies is within 6 dB of the peak amplitude.The 20 dB and 40 dB spectral bandwidths are also commonly used.

An example frequency spectrum 396 of imaging transducer 105 and anexample frequency spectrum 398 of angle detection transducer 100 areplotted in FIG. 6 such that the 6 dB points of both transducersintersect with the x-axis. Similarly, an angle detection pulse sent tothe angle detection transducer 100 will not cause a significant acousticresponse from the imaging transducer 105.

The frequencies of the two transducers may be selected to avoidharmonics of the transducer center frequencies. In general, it may beadvantageous to avoid having the center frequencies of the transducersas integral multiples of one another, so as to avoid confusion caused byharmonics from non-linear echoes. This is especially true for caseswhere microbubble specific imaging techniques are being used, as many ofthese techniques rely on harmonics for separation between tissue andcontrast agent. The higher frequency transducer may be configured tohave a larger absolute bandwidth to take advantage of increased axialresolution at the higher frequency, as shown.

In some circumstances, imaging excitation pulses may possess asignificantly broader bandwidth than that of the imaging transducer,thereby resulting in the possibility of transmitted pulses spectrallyoverlapping with the bands of both transducers. This may be mitigatedusing analog or digital filtering techniques to separate the effectivebands of the excitation pulses received by the individual transducers.

In one embodiment, such a filtering scheme may be implemented usingpassive elements as shown in FIG. 7. A filter 380 may be generated froma combination of electrical components, such as resistive, inductiveand/or capacitive components, and is employed to spectrally restrictimaging pulses from exciting the angle detection transducer 100, while afilter 390 may be generated from a combination of electrical componentsto spectrally restrict angle detection pulses from exciting the imagingtransducer 105. Alternatively, narrower band excitation pulses can beused for imaging, angle detection or both.

In another example embodiment, in which both transducers are spectrallyisolated as shown in FIG. 6, a broadband excitation pulse or waveformmay be provided that overlaps the spectral bandwidths of bothtransducers, or the excitation waveform may include a first spectralcomponent that is within the bandwidth of one transducer, and a secondspectral component that is within the bandwidth of another transducer.

Detected signals are demultiplexed in the frequency domain usingspectral filtering techniques to individually resolve the signalsdetected from each transducer. Spectral filtering of the detectedsignals may be implemented using either analog or digital filtering, orboth. For example, the signal from the single electrical channel can beseparated using analog filters to two separate receive channels that maybe connected to two separate analog to digital converters in imageprocessing and display system 49. Alternatively, digital spectralfiltering can occur on digitally sampled representation of the receivedsignal using a single analog to digital converter where digitalprocessing hardware or software, are used to separate the imaging andangle detection data.

FIG. 8 illustrates an embodiment in which tiltable member 150 isconfigured to reflect incident radiation from imaging transducer 105,and where the angular deflection of tiltable member 150 is detectedusing a time of flight method. In this case, imaging transducer 105 ismounted at a fixed location and oriented towards the tiltable member150.

As shown in the figure, another imaging transducer or imaging radiationsource 103 can be mounted adjacent to, attached to, or transmittingthrough a hole bored into the imaging transducer 105 as described in USPatent Publication No. 20080177183. For example, an optical imagingsource/receiver 103 could be mounted to ultrasound imaging transducer105 to provide a second imaging modality within an imaging probe. It isto be understood that it is not necessary that the front surface ofreflective tiltable member 150 is the same as the back surface of thereflector 153. The front surface 151 may be constrained to being highlyoptically and/or acoustically reflective, while it may be desirable forthe back surface 153 to be a diffuse acoustic reflector and/orscatterer.

FIGS. 8a and 8b illustrate a common embodiment with tiltable member 150shown at two different tilt angles, where tiltable member 150 isrotatably mounted on pivot axis 152. Angle detection transducer 100 isplaced at a fixed location relative to pivot axis 152. Imagingtransducer 105 transmits an acoustic beam 120, while optical imagingsource 103 transmits an optical beam 130, where both acoustic beam 120and optical beam 130 are transmitted in a direction towards the frontsurface 151. Angle detection transducer 100 transmits an acoustic beam110 towards the back surface 153 of tiltable member 150, and a portionof the beam is reflected back towards the angle detection transducer100. This may be achieved via diffusive reflection of the incidentultrasonic angle sensing beam.

In FIG. 8a , tiltable member 150 is relatively far from the angledetection transducer 100, along the path of beam 110, when compared toFIG. 8b . This results in the angle detection beam 110 having a shortertime of flight in FIG. 8b than FIG. 8a . The tilt angle can becalculated as described above in reference to FIG. 4. Timing diagramsare presented for each angle scenario. A pulse is transmitted at t=0with a high amplitude and received at a later time, typically with areduced magnitude. FIG. 8e shows a sample plot of time delay, or time offlight vs. imaging angle. FIGS. 8c and 8d are timing diagrams arepresented for each angle scenario in FIGS. 8a and 8b , respectively. Thereceived pulse 502 corresponding to the signal from FIG. 8a has a muchgreater time delay that the received pulse 504 corresponding to thesignal from FIG. 8 b.

FIGS. 9a-9e illustrate an embodiment in which the change in angle of atiltable member, such as ultrasonic imaging transducer 105 is detectedusing a time of flight method. This embodiment is similar to that ofFIG. 7, except that ultrasonic imaging transducer 105 is not mounted ona pivoting axis, and is instead mounted on a deformable member 112 whosedeformation is responsible for the tilting of the tiltable member.

FIGS. 10a-10e illustrates an embodiment in which the change of angle oftiltable member 101 (shown as an imaging transducer) is detected using asignal intensity method. This method is based on the relationshipbetween the intensity of diffusively scattered ultrasonic radiation andthe tilt angle, where the reflected signal will be strongest when theangle detection beam 110 is perfectly normal to tiltable member 101, asshown in FIG. 10a . As the tilt angle changes from normal, the strengthof the received signal is reduced (item 504 vs. item 502), as is seen inFIGS. 10c and 10d . The reduction in received signal intensity orvoltage can be used to estimate the tilt angle, as shown in the examplecalibration curve provided in FIG. 10 e.

FIGS. 10c and 10d are timing diagrams presented for each angle scenarioin FIGS. 10a and 10b , respectively. It is noted that there may betemporal broadening of the signal due reflections coming from differentslightly different depths as the imaging transducer 101 is moved awayfrom being normal to the angle detection beam 110. Such an effect isshown in FIG. 10d . Accordingly, in selected embodiments, the relativetemporal broadening may also be employed to provide feedback relating tothe deflection angle. Such an embodiment may be used to confirm and/orimprove the accuracy of the deflection angle obtained through intensitymeasurements.

In some embodiments, the sensitivity of angle detection may be hinderedat large deflection angles due to intensity reduction, as illustrated inFIG. 10. The intensity of a received signal from a perfect reflectordrops very quickly from angles even slightly off normal from the angledetection beam 110. This makes the signals very difficult to detect, anddiffusive reflectors may provide improved performance. There are severalpotential approaches to overcoming this.

The difference between a specular and diffusive reflector is illustratedin FIGS. 11a-d . FIG. 11a shows a specular reflective tiltable member170 receiving an angle detection beam 110 from an angle detectiontransducer 100. The beam is reflected off the specular reflector 170,and the reflected beam 113 is directed in a path that is not co-incidentwith the angle detection transducer. The result, as shown in the timingdiagram below in FIG. 11c , is that the pulse is not received.

FIG. 11b illustrates an embodiment in which the incident beam 110 isreflected by a diffusive reflector. While a portion of the beam 117 maybe directed away in a similar fashion as described in FIG. 11a , asignificant portion of the beam 115 is scattered and diffusivelyreflected over a wide angular range. A portion of this beam is collinearwith the incident beam 110, thus allowing for a time of flight detectiontechnique to be feasible (as shown in FIG. 11d by the presence of thereflected pulse).

Another potential arrangement that can assist with the reduction ofsignal from a substantially specular reflector is the use of multipleangle detection transducers. Such an embodiment is illustrated in FIGS.12a-12d . Here, two angle detection transducers 100, 126 are orientedtowards tiltable member 101 which is mounted on pivot axis 102. Each ofthe angle detection transducers 100, 126 generate their own acousticbeam 110, 127.

All 3 transducers of the preceding embodiment may be driven by a singleelectrical channel (for example, connected to patient interface module36 of FIG. 1). Notably, there will be an overlap in the received signalsfrom the angle detection transducers 100, 126 if they lie within thesame frequency range. This can be resolved with prior knowledge of thetransducer positions, or by limiting the range of angles through whichthe tiltable member is allowed to tilt.

The distance calculated by the time of flight difference between the tworeceived pulses may provide tilt angle information in this case. Forinstance, if the two angle detection transducers 100, 126 are placed 90°from each other with one of the beams parallel to the longitudinal axis,equidistant from pivot axis 102 and on opposing sides of pivot axis 102but the same side of tiltable member 101 with a flat surface (as theyare in FIG. 12), the difference in the time between the received pulsesfrom both transducers will be at a minimum when the tilt angle is 45°from the longitudinal axis (As suggested by FIGS. 12c and 12d ). As thetilt angle moves away from 45°, the time between the received signalsbetween the two transducers will increase, as shown in FIG. 12d withreceived pulses 510, 512 from angle detection transducers 100, 126respectively.

Angle sensing transducers 100 and 126 may be selected to havesubstantially non-overlapping spectral bandwidths, thus allowing theindividual detected signals to be separated based on their frequencydomain content. Alternatively, one of the angle sensing transducers maybe placed further away from tiltable member 101 than the other, thusensuring that the time delays from each of the angle sensing transducersis distinct from the time delay detected by the other angle sensingtransducer.

Alternatively, knowledge of the expected direction and/or degree of tiltof the tiltable member can be used to algorithmically determine whichportions of the sensed signal along the single electrical channelcorrespond to each of the two or more angle sensing transducers. Forexample, in the example implementation of an imaging probe having amovable member with an angular orientation that is dependent on therotational speed of a rotational conduit housed within the imagingprobe, if the rotational speed of imaging assembly 50 along thelongitudinal axis of imaging probe 44 is increased, it may be expectedthat the tiltable member would tilt in a more forward looking direction.Therefore, knowledge of the expected direction of tilt could be used toidentify which of the peaks in the received signal corresponds to one ofthe several angle sensing transducers. Similarly, knowledge of theinstantaneous rotational velocity of the imaging assembly may correspondwith a greater likelihood to a particular range of tilt angles, and sucha relationship could be used to identify which of the peaks of thereceived signal most likely corresponds to one of the several anglesensing transducers.

FIGS. 13a-13e illustrates an embodiment that enables sensitive angulardetection while increasing the range of angles that can be detected bythe angle detection transducer 100. In this embodiment, the back surfaceof tiltable member 183 (which may also include an imaging transducer, asshown in FIG. 13) has been shaped with a series of curved indentations.As the transmitted beam 110 hits the back of tiltable member 183, asmall portion of the reflective interface will be substantially normalto the incident beam 110, causing part of the beam 181 to be reflectedback to angle detection transducer 100. Accordingly, the angle can beresolved using a time of flight method similar to FIG. 4. It is to beunderstood that the specific cylindrical surface patterning illustratedin FIG. 13 is merely one non-limiting embodiment, and that a wide rangeof surface profiles may be employed to achieve a similar resultaccording to the present embodiment. For example, paraboliccross-sections, or a pattern of divots may be used on the back surfaceof tiltable member 183.

While the preceding embodiments have disclosed surfaces that arediffusively reflective, it is to be understood that diffusivereflections may be generated by surface and/or volume materialproperties. For example, particles of metals, ceramics, silicon dioxide,graphite, glass beads, or other compounds known in the art can be addedto a material or surface to make it more diffusely reflective.

The use of composite materials or flexible polymers has allowed forultrasound imaging transducers to be shaped physically. Such transducersmay be employed for focusing acoustic energy. Alternatively, acousticlenses may also be used to focus acoustic energy. However, such schemesmay be adapted to the present embodiments to broaden the acoustic beamand support an increase in the range of angles that can be detected.This is illustrated in FIGS. 14a-14d , where angle detection transducer200 is curved such that it creates diverging beam 210. As shown in theFigure, a portion of the beam is normal to the imaging transducer 101 ata wide range of angles. The normal portion of the beam 220 is reflectedback to the transducer, even when the tiltable member is a specularreflector, and may be measured to estimate tilt angle using a time offlight method as in FIG. 4.

Yet another embodiment for increasing the range of angles that can bedetected may be achieved by attaching the angle detection transducer tothe tiltable member. FIGS. 15a-15e shows an example of one suchembodiment. In this embodiment, angle detection transducer 100 ismounted to the back of the tiltable member 101. The angle detection beam110 is directed towards stationary reflector 174. A portion ofstationary reflector 174 may be curved (in any of several shapes) toprovide a suitable angle-dependent acoustic reflection profile. Exampleyet non-limiting curvature profiles include circular, elliptical orparabolic shapes.

In one embodiment, the stationary reflector 174 may be shaped so thatover a wide range of imaging transducer 101 tilt angles, the reflectionfrom the angle detection beam 110 is largely retro-reflected towards theangle detection transducer 100. As shown in FIGS. 15c and 15d , one orboth of the time of flight and intensity schemes may be employed toinfer changes in the orientation of tiltable member 101.

FIG. 15e describes one method to design a stationary retroreflectingacoustic reflector. The angle detection transducer 100 is modeled in aforward viewing position, as defined by tilt axis 600. A desireddistance 608 between angle detection transducer 100 and the reflectingsurface is chosen and a data point is generated on a line normal totransducer 100 a distance 608 away from transducer 100. The angledetection transducer is tilted by angle 616 about pivot point 102 anddesired distance 610 between angle detection transducer and reflectingis chosen to differ from 608 by a selected amount, such as an amount forobtaining a desired angular resolution. A data point is generated aswith the above. This process is repeated until the angle detectiontransducer is tilted to the point that it is side viewing. A continuoussurface 601 is defined by interpolating the data points generated asdescribed above using known curve fitting techniques. Examples ofsuitable curves that can be fitted are portions of an ellipse, parabola,circle, hyperbola, exponential, roulette, or polynomial using fittingstrategies common in the art including but not limited to ordinary leastsquares or total least squares.

Once a surface is defined and fabricated, there may be imperfections inmachining tolerances and misalignments in assembly among otheruncertainties. In order to mitigate this, calibration of an angledetection assembly may be used to overcome these imperfections.

According to another embodiment, the surface 601 is defined such thatthe angle detection beam emitted by the angle sensing ultrasonictransducer 100 is substantially retroreflected over a given range ofpivot angles, such that the distance between surface 601 and anglesensing ultrasonic transducer 100 varies monotonically over the range ofpivot angles, and such that the rate of change of the relative distancewith respect to the pivot angle (which, at least in part, determines theresolution of the apparatus), exceeds a minimum value over the range ofpivot angles. In one embodiment, surface 601 is configured such that therate of change of the relative distance with respect to the pivot angleis substantially constant over the range of pivot angles, such that thesensitivity of the apparatus is substantially independent of pivot angleover the range of pivot angles.

As noted above, in some embodiments, the angle of the detection beam maybe constrained to remain approximately normal to the reflective surfaceof the tiltable member, thereby generating a retroreflection. Thiseliminates the need to compensate for reflections at angles where theangle detection beam is not normal to the tiltable member, and generallyresults in detected beam of higher intensity. Example embodimentsutilizing such an approach are shown in FIGS. 16 and 17. FIGS. 16 a-dillustrate an embodiment in which angle detection transducer 100 ismounted onto second tiltable member 114 that is mechanically linked orcoupled to first tiltable member 101 via coupling mechanism 176.Secondary tiltable member 114 is not necessarily acoustically active(and may be acoustically passive) and allowed to pivot about axis 104.

Since both members are able to pivot about their own pivot axes and aremechanically coupled, they will tilt in unison. The tiltable members aremechanically coupled such that they tilt with a substantially equal tiltangle during operation. A number of techniques may also be used tocouple the motion of the tiltable members, including, but not limitedto, rods, beams, magnets, and electromagnetic devices. The embodimentsshown in FIGS. 16 and 17 have the additional benefit of adding anothertiltable member to the system that may not suffer from inertial or otherdesign constrains of the first tiltable member, such as being anultrasound transducer optimized for acoustic performance.

Such a scheme may be useful in cases where first tiltable memberincludes an ultrasonic imaging transducer, but does not possess suitablecharacteristics for external rotational actuation. By incorporatingsecondary tiltable member 114 with characteristics designed foractuation via external rotation and mechanically linking both tiltablemembers, first tiltable member 101 can be actuated based the behavior ofsecond tiltable member 114. For example, as shown in FIGS. 4f and 4g ,ultrasound transducers may have similar or larger dimensions in therange direction compared to the elevation directions. This is largelydue to the requirement for backing on an ultrasound transducer toattenuate signals in directions other than the desired imagingdirection. Bodies of this geometric configuration are not ideal foractuation via external rotation, as shown in FIGS. 4f and 4 g.

FIG. 4f shows a body 134 that has a similar dimension in the rangedirection relative to the elevation direction. Here, the body pivotsabout point 137 under rotation in direction 63. If the body is brokeninto two components, one above longitudinal axis 131 and one below, thecenter of mass of the components above and below longitudinal axis 131are shown at 136 and 133 respectively. The centripetal force vectors areshown as 135 and 132 respectively.

Now, comparing to a body shown in FIG. 4g , where the dimension in therange direction is much smaller than the dimension in the elevationdirection, we see similarly that the body pivots about point 121 underrotation in direction 63. If the body is broken into two components, oneabove longitudinal axis 122 and one below, the center of mass of thecomponents above and below longitudinal axis 122 are shown at 124 and128 respectively. The centripetal force vectors are shown as 129 and 123respectively. The result is that the pivotally mounted body 125 in FIG.4g has a much stronger relative component of centripetal force (andtherefore a larger applied torque) that acts to cause tilt about thepivot point 121 than body 134 does about pivot point 137. Accordingly,in some embodiment, an imaging probe may include first and seconddeflectable members that are mechanically coupled, where the first andsecond deflectable members are configured such that centripetal forcesgenerated by rotation of the imaging assembly apply a larger torque tothe second deflectable member about a tilt axis of the seconddeflectable member than to the first delectable member about a tilt axisof the first deflectable member.

This mechanical coupling may also allow angle detection beam 110 toremain normal to the ultrasound imaging transducer 101. Other techniquesthat additional deflectable member can employ to assist in deflectionmay include the use of hydrofoil features or artificial muscleactuation.

A time of flight technique can be used to estimate the imaging angle,similar to that shown in FIG. 4. Alternatively, or additionally, anintensity measurement method may be employed, as illustrated in FIGS.10c and 10 d.

FIG. 16e illustrates some of the parameters that may be employed tocalculate the tilt angle θ based on measured distance 400. If thedistance 401 between acoustically passive disc 114 and the imagingtransducer 101 is constant and known a priori, and the distance betweenthe angle detection transducer 100 and the imaging transducer 101 isdetermined with the knowledge of the signal time of flight and the speedof sound in the medium, the angle can be calculated with thetrigonometric equation θ=arcCos(measured_distance 400/known_distance401).

In a similar embodiment, illustrated in FIGS. 17a-17d , angle detectiontransducer 100 can be mounted on the tiltable member 101, and maintainedin a normal orientation relative to acoustically passive tiltable member114. A unitary structure similar to that shown in FIG. 5a would besuitable for use as the tiltable member 101 in FIG. 17 a.

FIG. 18a illustrates an embodiment that combines the features shown inFIGS. 15 and 17. Here, the stationary curved reflector 174 is employedto increase the range of angles that can be detected using the angledetection transducer 100. This is achieved by separating the imagingtransducer 101 and the acoustically passive tiltable member 114 in spacesufficiently such that they do not come into contact with each otherregardless of tilt angle (within the range permitted during operation),while still allowing the acoustically passive second tiltable member 114to be employed to assist the ultrasound imaging transducer 101 inachieving desired motion using mechanical coupler 176.

FIG. 18b shows a view cut of an example embodiment through the hatchedline in FIG. 18a . A notch 177 in the stationary curved reflector 174 iscreated such that the mechanical coupler 176 is allowed to pass throughthe stationary reflector 174 unimpeded. By way of example, mechanicalcoupler 176 may include a simple bar or rod that is connected to each ofthe tiltable members 114 and 101 by a hinge or other mechanism, such asa mechanism that creates a pivot point or deformable joint betweenmechanical coupler 176 and each of the tiltable members.

FIGS. 18 c-i demonstrate another apparatus for detecting tilt anglewhere the angle detection transducer 100 is mounted inside the notch 177of supporting structure 175 instead of being attached to the tiltablemember 101. FIGS. 18c and 18e show the setup at two different tiltangles. Cut view through the hatched lines in FIGS. 18c and 18e areshown in FIGS. 18d and 18f respectively. FIGS. 18g and 18h show thetiming diagrams for FIGS. 18d and 18f respectively. In FIG. 18d , themechanical coupling bar 176 is near the top of the notch 177 resultingin the received signal in 18 g having a long delay, whereas in FIG. 18fit is considerably further down within the notch, and is subsequentlycloser to the angle detection transducer resulting in a received signalwith a shorter time delay. FIG. 18i shows a plot estimating deflectionangle vs. time delay. Alternatively, the angle detection transducer 100can be mounted on mechanical coupling bar 176 and pointed towards thebottom of notch 177.

FIGS. 18c-i show how a second transducer 100 can be used to detect theposition of a component within an imaging probe. While the positioninformation may be used to infer the tilt angle of a tiltable component,the ability to more generally gather information about the position of amovable component within an imaging probe by using a second transducerthat shares a common single channel with another ultrasound transducerbecomes apparent.

Although FIG. 18 provides one example embodiment in which an additionalultrasonic transducer is employed for detecting changes in a position ofa movable component, it is to be understood that this embodiment may beemployed in a wide number of applications for detecting motion of acomponent within an ultrasonic probe. Other illustrative examples inwhich the motion of a component may be detected include features in thesheath during a pullback operation, a retractable sheath, the presenceof bubbles, a change in fluid density in the catheter, or a therapeutictool such as a Brockenborough needle.

Accordingly, it is to be understood that the scope of the embodimentsdisclosed herein is not to be limited to those in which an angularorientation or a change in an angular orientation of a movable componentis determined using one or more additional ultrasonic transducers, andfurther encompasses embodiments in which a position or a change inposition of a movable component is determined using one or moreadditional ultrasonic transducers, irrespective of whether or not theposition or change in position relates to an angular orientation or achange in angular orientation.

FIG. 19 shows an example time-domain imaging and angular detectionsequence for a single pulse-echo ultrasound imaging sequence using theembodiment described in FIG. 17. In FIG. 19a , imaging transducer 101 isexcited with a low frequency pulse, as shown in the timing diagram shownin FIG. 19b . The pulse generates an acoustic beam 120 which propagatesuntil it reaches an object 106 in its path.

Part of the beam is reflected, and detected by the imaging transducer,and as a result displayed in the “Receive” portion of the timingdiagram. Next, the residual beam meets another object 108, and again, apart of the beam is reflected, and detected by the imaging transducerand likewise appears as a received signal, slightly further along the“Receive” timing diagram.

After imaging data is received, a high frequency angle detection pulseis transmitted down the same channel, generating an acoustic beam 110from the angle detection transducer 100. This beam is reflected off theacoustically passive member 114 and returned to the transducer. The tiltangle is determined using the time of flight of the beam 110 followingthe high frequency pulse generation.

As described above, this embodiment can be optionally aided with the useof one or more electronic filters to select the desired frequencycomponents. For example, a low pass filter may be used to emphasize lowfrequency signals from the low frequency imaging transducer 101following transmission of an imaging pulse 550, while a high pass filtermay be used to emphasize the high frequency signals from high frequencyangle detection transducer 100 following the transmission of angledetection pulse 500. These filters may reside within the imaging probe,or optionally external to the imaging probe, such as within controllerand processing unit 34 or patient interface module 36.

FIG. 19c-e shows an embodiment where both transducers are excited with abroadband pulse that covers the bandwidths of both imaging transducer101 and angle detection transducer 100. The received signal from bothtransducers is demultiplexed in order to separately process the imagingsignal data and the angle sensing data. Such demultiplexing may beachieved according to one of many embodiments.

In one such discriminatory embodiment, as described in FIG. 19d , a timedomain method is employed utilizing the fact that there may be asignificant difference in the distance between a) the angle detectiontransducer 100 and the second deflectable member 114 and b) the imagingtransducer 101 and the acoustic imaging targets 106 and 108. Thedistance between the angle detection transducer 100 and the seconddeflectable member 114 may be significantly less than the distancebetween the imaging transducer 101 and the acoustic imaging targets 106and 108. In this arrangement, signals received 558 shortly aftertransmission 560 pulse is sent may be deemed to be as a result of theangle detecting transducer 100, and signals received after later timedelays 554, 556 may be deemed to be as a result of the imagingtransducer 101. Accordingly, in such an embodiment, all pulses receivedprior to the vertical hatched line 562 are deemed to be angle detectionpulses and those received after are deemed to be imaging pulses.

A second embodiment for demultiplexing the signals may be achieved byspectrally filtering or separating the spectral content contained withinthe net signal and can be achieved using the same embodiment shown inFIG. 19c . A representative timing diagram is shown in FIG. 19d asdescribed above. Since the bandwidths of the transducers aresufficiently separated and may be known, signals falling within thebandwidth of the angle detection transducer 100 can be deemed to beoriginating from the angle detection transducer 100, and signals fallingwithin the bandwidth of the imaging transducer can be deemed to beoriginating from the imaging transducer.

This spectral separation is shown the spectral plot in FIG. 19e , wherethe vertical hatched line 564 is used to show a point representing theseparation between imaging data and angle detection data. This line maybe the midpoint between the center frequencies of the two transducers.All spectral components lower than the frequency represented by thehatched line are deemed to be components of the imaging signal 568, andall spectral components higher than the frequency represented by thehatched line are deemed to be components of the angle detection signal.Also, the separation may be defined more than a single line. Forinstance, the −6 dB, −20 dB or −40 dB bandwidths may be used as pointsto separate data between angle detection and imaging. Furthermore, theboth the time of flight demultiplexing and spectral demultiplexingtechniques described for FIG. 19c-e above can be combined.

It is to be understood that there are many methods that can be employedto obtain sufficient spectral isolation of the two signals. As describedabove, filtering techniques may be employed to separate the spectralsignals received from each transducer. In another embodiment, spectralwindows corresponding to each transducer may be determined based on anisolation criteria. For example, the upper end of the spectral windowfor the lower-frequency transducer may be selected as corresponding tothe point at which the spectral response of the higher-frequencytransducer falls below a desired value (for example, 20 dB).

In some situations, it may be desirable to excite the ultrasoundtransducers at different points in time, with differing repetitionfrequencies. One example of this is where one of the transducers isconfigured for angle detection. In this scenario, changes in angle maybe extremely minute such that it may be unnecessary to perform angledetection with at the pulse repetition rate required for imaging. Forexample, it may be that the angle is expected to remain relativelyconstant over the amount of time required to acquire multiple imagingvectors. A pulse sequence can be defined such that imaging pulses 550are transmitted and acquired much more frequently than angle detectionpulses 500, as shown in FIG. 19 f.

Similarly, it may be desirable in some situations to allow more time forecho return from one ultrasound transducer than the other. One exampleof this is where one of the transducers is configured for angledetection. In this scenario, it is often the case that the transducerconfigured for angle detection is of higher frequency that thetransducer configured for imaging. Furthermore, it is often the casethat the angle detection is performed using echoes from locations thatare spatially very close to the angle detection transducer, requiringrelatively little acquisition time to ensure capture of echoesassociated with angle detection.

This scenario is illustrated in FIG. 19g . Imaging pulse 550 istransmitted and a relatively long period of time 420 is dedicated towaiting for echoes associated with imaging pulse 550. Conversely,relatively little time 422 is dedicated to waiting for echoes associatedwith angle detection pulse 500.

In some embodiments, the temporal spacing between imaging pulses may beconfigured to be variable. By way of example, in situations where amotor encoder is used as a trigger for imaging pulses, the imaging pulserepetition frequency will be higher the motor is rotating more quicklythan when the motor is rotating more slowly. Accordingly, the pulserepetition frequency for angle detection may also be selected to bevariable, and to be determined by the pulse repetition frequency ofimaging.

It is to be understood that FIGS. 4, and 8 through 19 representembodiments that are typically housed within the imaging assembly 50,but that the other components of the imaging assembly are not shown forsimplicity.

FIG. 20 illustrates three different techniques for calculating therelative distance travelled by the ultrasonic angle sensing beam, basedon the detected radio-frequency (RF) signals. The first method, shown inFIG. 20a , involves calculating the peak value of the RF signal for eachpulse. As shown, the received electronic pulse includes a pulse envelopeand oscillations of a carrier wave. The first pulse 402 is shown asarriving relatively early compared to the second pulse 404. This impliesthat the angle detection transducer 100 is closer to the tiltable member101, with the first pulse 402 (for example, as shown in FIG. 4b ) thanthe second pulse 404 (for example, as shown in FIG. 4a ). The difference414 between the peak RF value 406 from the first signal and the secondsignal 408 can be used to estimate the distance between the two pointswhich can then be used to infer the tilt angle.

However, the RF signal in the carrier wave can fluctuate significantlyas a result of minor changes in sub-resolution scatterers, and itfollows that using the RF peak detection method can lead to inaccuracieswhen measuring small changes in position. For example, if a new peakemerges, there will be significant error in the measurement of distancebetween the angle detection transducer and the imaging transducer.

Another approach is to first calculate the envelopes of signals (407 and409 for RF signals 402 and 404 respectively) and using the difference416 between the envelope peaks (410 and 411 for envelopes 407 and 409respectively) to estimate distance. Some of the fluctuation issuesdescribed with using the RF peak method are eliminated with thistechnique.

Another example employs the cross correlation between two signals toestimate the distance between subsequent received RF pulses. An exampleembodiment is shown in FIG. 20b . The cross correlation between thefirst 402 and second 404 RF pulses is shown as 413, with the peak of thecross correlation signal being detected as 412. The amount of timebetween time 0 and the peak value is given as 418 and can be used tocalculate the distance travelled between two tilt angles to calculateangular shift.

Generally, the cross-correlation may be performed between a given pulseand another recorded pulse, such as a previously recorded pulse obtainedat a different angular tilt. Alternatively, the cross correlation may beperformed between a given pulse and a pulse stored at time ofcalibration of the imaging probe and retrieved from the EEPROM or othermemory mechanism associated with imaging probe 44. Alternatively, thecross correlation may be performed between a given pulse and astandardized pulse for a particular design of imaging probe 44, assumingthat the pulses generated by the angle detecting transducer areadequately reproducible between imaging probes fabricated from the samedesign.

In the preceding angle-detection embodiments, outliers may be detectedand rejected to improve the performance angle detection. There areseveral known techniques for rejecting outliers which could be appliedincluding statistical techniques and voting methods. FIG. 21 showsexperimental measurements of using an angle detection schemecorresponding to the embodiment described in FIG. 18a . Distancesbetween two tiltable disc-shaped members were calculated using thecross-correlation method from FIG. 20b . The tiltable members weretilted using a microstage that continuously advanced a rod against thesurface of one of the tiltable members causing the two tiltable membersto tilt in unison. The position of the rod (in microns) is shown on thex-axis. The normal distance measured between the two tiltable members asmeasured by an angle detecting transducer on one of the tiltable membersis shown on the y-axis (in microns), as depicted in FIG. 17. The tiltangle subtended by the tiltable members with an arbitrary axis could becalculated at each time point based on the measured distance between thetwo members. This angle was compared to the expected angle based on asolid model.

The specific embodiments described above have been shown by way ofexample, and it should be understood that these embodiments may besusceptible to various modifications and alternative forms. It should befurther understood that the claims are not intended to be limited to theparticular forms disclosed, but rather to cover all modifications,equivalents, and alternatives falling within the spirit and scope ofthis disclosure.

Therefore what is claimed is:
 1. An imaging probe comprising: alongitudinal body; an imaging assembly housed within said longitudinalbody; a first ultrasonic transducer provided within said longitudinalbody, wherein said first ultrasonic transducer is located remote from aproximal end of said longitudinal body, and wherein said firstultrasonic transducer is configured to deliver an ultrasonic imagingbeam to a region outside of said longitudinal body and to receivereflected ultrasonic imaging energy from the region, and wherein saidfirst ultrasonic transducer is provided within said imaging assembly; asecond ultrasonic transducer housed within said longitudinal body; and afirst electrical path and a second electrical path extending throughsaid longitudinal body, said first electrical path and said secondelectrical path defining a common electrical channel; wherein said firstultrasonic transducer and said second ultrasonic transducer are eachconnected to said first electrical path and said second electrical path,and wherein said first electrical path and said second electrical pathare electrically connectable to an image processing system; wherein saidimaging assembly includes a movable member for scanning an angularorientation of the ultrasonic imaging beam; wherein said secondultrasonic transducer is an angle sensing ultrasonic transducerconfigured for generating an angle sensing ultrasonic beam andgenerating an angle sensing signal associated with an angularorientation of said movable member relative to a longitudinal axis ofsaid longitudinal body; and wherein said imaging assembly furtherincludes an acoustically reflective substrate, wherein said anglesensing ultrasonic transducer is configured to direct the angle sensingultrasonic beam towards said acoustically reflective substrate and toreceive a reflected ultrasonic beam reflected from said acousticallyreflective substrate, wherein the angle sensing signal is produced bysaid angle sensing ultrasonic transducer in response to the reflectedultrasonic beam, wherein the angle sensing signal is detectable on saidcommon electrical channel.
 2. The imaging probe according to claim 1wherein said acoustically reflective substrate is positioned relative tosaid movable member such that a change in an orientation of said movablemember relative to a longitudinal axis of said longitudinal bodyproduces a change in the angle sensing signal.
 3. The imaging probeaccording to claim 2 wherein said acoustically reflective substrate isconfigured such that the change in the angle sensing signal includes arelative time delay of the angle sensing signal.
 4. The imaging probeaccording to claim 2 wherein said acoustically reflective substrate isconfigured such that the change in the angle sensing signal includes achange in one or more of an intensity of the angle sensing signal and aspectral content of the angle sensing signal.
 5. The imaging probeaccording to claim 2 wherein said movable member includes saidacoustically reflective substrate and wherein an orientation of saidangle sensing ultrasonic transducer is fixed relative to said imagingassembly.
 6. The imaging probe according to claim 2 wherein said anglesensing ultrasonic transducer is attached to said movable member, andwherein an orientation of said acoustically reflective substrate isfixed relative to said imaging assembly.
 7. The imaging probe accordingto claim 6 wherein said movable member is a pivotable member, andwherein said acoustically reflective substrate includes a curved surfaceprofile, wherein a curvature of said curved surface profile is selectedsuch that a deflection of said movable member produces a change in arelative time delay of the angle sensing signal.
 8. The imaging probeaccording to claim 7 wherein said curved surface profile is selectedsuch that a distance between said angle sensing ultrasonic transducerand said acoustically reflective substrate, as determined along a beampath of the angle sensing ultrasonic beam, varies over a defined angularrange of said pivotable member.
 9. The imaging probe according to claim8 wherein said curved surface profile is selected such that a rate ofchange of the distance relative to a pivot angle of said pivotablemember exceeds a minimum value over the defined angular range.
 10. Theimaging probe according to claim 9 wherein said curved surface profileis selected such that the rate of change of the distance relative to thepivot angle of said pivotable member is substantially constant over thedefined angular range.
 11. The imaging probe according to claim 2wherein said first ultrasonic transducer and said angle sensingultrasonic transducer form at least a portion of said movable member.12. The imaging probe according to claim 2 wherein said movable memberincludes a first deflectable member mechanically coupled to a seconddeflectable member, such that a change in an orientation of said firstdeflectable member produces a corresponding change in an orientation ofsaid second deflectable member, and wherein a change in the orientationof said second deflectable member produces a change in the direction ofthe ultrasonic imaging beam.
 13. The imaging probe according to claim 12wherein said second deflectable member is configured such thatcentripetal forces generated by rotation of said imaging assembly applya larger torque to said second deflectable member about a tilt axis ofsaid second deflectable member than to said first deflectable memberabout a tilt axis of said first deflectable member.
 14. The imagingprobe according to claim 13 where said second deflectable member isdesigned to have a dimension in an elevation direction that is largercompared to the dimension in a range direction.
 15. The imaging probeaccording to claim 12 wherein said angle ultrasonic transducer isattached to one of said first deflectable member and said seconddeflectable member, and wherein another of said first deflectable memberand said second deflectable member includes said acoustically reflectivesubstrate.
 16. The imaging probe according to claim 12 wherein saidmovable member further includes a coupling member for mechanicallycoupling said first deflectable member and said second deflectablemember, said coupling member having said angle sensing ultrasonictransducer mounted thereon, and wherein said acoustically reflectivesubstrate is positioned relative to said coupling member such thatmotion of said coupling member produces the change in the angle sensingsignal.
 17. The imaging probe according to claim 12 wherein said anglesensing ultrasonic transducer is attached to one of said firstdeflectable member and said second deflectable member, and wherein saidacoustically reflective substrate is fixed relative to said movablemember.
 18. The imaging probe according to claim 2 wherein said anglesensing ultrasonic transducer is positioned such that the angle sensingultrasonic beam is constrained to be directed approximately normal to asurface of said acoustically reflective substrate.
 19. The imaging probeaccording to claim 2 wherein said first ultrasonic transducer forms atleast a portion of said movable member.
 20. The imaging probe accordingto claim 2 wherein said acoustically reflective substrate is configuredsuch that the reflected ultrasonic beam includes a non-specularreflection of the angle sensing ultrasonic beam.
 21. The imaging probeaccording to claim 20 wherein said acoustically reflective substrateincludes a textured surface.
 22. The imaging probe according to claim 21wherein said textured surface is a diffusive reflective surface.
 23. Theimaging probe according to claim 21 wherein said textured surfaceincludes a periodic spatial profile.
 24. The imaging probe according toclaim 20 wherein a volume of said acoustically reflective substrateincludes a diffusive reflective material.
 25. The imaging probeaccording to claim 2 wherein said angle sensing ultrasonic transducer isconfigured for emitting the angle sensing ultrasonic beam with adivergent beam profile.
 26. The imaging probe according to claim 2wherein said angle sensing ultrasonic transducer is a first anglesensing ultrasonic transducer, said imaging assembly further includingan additional angle sensing ultrasonic transducer configured to directan additional angle sensing ultrasonic beam towards said acousticallyreflective substrate and to generate an additional angle sensing signalby detecting an additional reflected ultrasonic beam reflected from saidacoustically reflective substrate, and wherein said additional anglesensing ultrasonic transducer is connected to said common electricalchannel.
 27. The imaging probe according to claim 26 wherein a centerfrequency of said additional angle sensing ultrasonic transducer issubstantially different from the center frequency of said first anglesensing ultrasonic transducer.
 28. The imaging probe according to claim26 wherein a center frequency of said additional angle sensingultrasonic transducer is substantially the same as the center frequencyof said first angle sensing ultrasonic transducer.
 29. An imaging systemcomprising: the imaging probe according to claim 2; and a delivery anddetection subsystem for delivering electrical energy to said firstultrasonic transducer and said angle sensing ultrasonic transducer, andfor detecting electrical signals detected by said first ultrasonictransducer and said angle sensing ultrasonic transducer.
 30. The imagingsystem according to claim 29 wherein said first ultrasonic transducerand said angle sensing ultrasonic transducer are each characterized bynon overlapping spectral bandwidths, and wherein said delivery anddetection subsystem is configured for delivering broadband electricalenergy to said first ultrasonic transducer and said angle sensingultrasonic transducer such that a spectrum of the broadband electricalenergy overlaps a spectral bandwidth of said first ultrasonic transducerand said angle sensing ultrasonic transducer.
 31. The imaging systemaccording to claim 30 wherein said delivery and detection subsystemfurther includes a processor, wherein said processor is programmed todetermine, based on the change in the angle sensing signal, acorresponding change in a direction of the ultrasonic imaging beam. 32.The imaging system according to claim 31 wherein said processor isprogrammed to control a direction of the ultrasonic imaging beam basedon feedback from the angle sensing signal.
 33. The imaging systemaccording to claim 29 wherein said first ultrasonic transducer and saidangle sensing ultrasonic transducer are each characterized by nonoverlapping spectral bandwidths, and wherein said delivery and detectionsubsystem is configured for delivering electrical energy to said firstultrasonic transducer and said angle sensing ultrasonic transducer suchthat a spectrum of the electrical energy includes a first spectralcomponent within a spectral bandwidth of said first ultrasonictransducer and a second spectral component within a spectral bandwidthof said angle sensing ultrasonic transducer.